نوع مقاله : مقاله پژوهشی

نویسندگان

• زهرا ربیعی غفار ¹
• حسین عساکره ²
• یونس خسروی ³

¹ دانشجوی دکتری آب و هواشناسی، دانشگاه زنجان، زنجان، ایران

² استاد اقلیم شناسی ،دانشگاه زنجان، زنجان ، ایران

³ دانشیار علوم محیط زیست ، دانشگاه زنجان ، زنجان ، ایران

چکیده

نمودها و جلوه های تغییرات اقلیمی، به عنوان یکی از واقعیت­ های طبیعی، به طور آشکاری قابل ردیابی است. این رویدادها به شکل ناهنجاری و یا نوساناتی در فراسنج های اقلیمی نظیر بارش، دما وغیره ایجاد می ­شوند. به منظور بررسی تغییرات دهه­ ای احتمال تداوم بارش ایران زمین طی چهار دهه اخیر (سال 1355 تا 1394) از پایگاه داده اسفزاری نسخه سوم حاصل میان یابی داده های بارش روزانه 2188 ایستگاه همدید، اقلیمی و باران سنجی سازمان هواشناسی به مدت 46 سال از1349 تا 1394 استفاده شد. ابتدا روز بارانی براساس روشی نوین تعریف شد. سپس احتمال تداوم بارش طی دوره آماری 1394-1349 از طریق زنجیره مارکوف بدست آمد. نتایج نشان داد بیشترین احتمال تداوم ­و تغییرات آن ­طی تداوم یک تا هفت روزه بارش در ساحل غربی و شرقی خزر و شمال غرب ایران و جنوب البرز­ دیده شده است. پهنۀ وسیعی از ایران احتمال رخداد بارش یک روزه و تداوم دو روزه بارش را تجربه کرده اند. در تداوم های بالاتر میزان درصد احتمال پهنه های زیر پوشش کاهش می­ یافت. طی دهه آخر -سال 1385 تا سال 1394- گسترۀ تغییرات نواحی نسبت به سه دهه قبلی بیشتر بود. کم­ترین میزان تغییرات مربوط به جنوب ایران است. ­میزان درصد احتمال تغییرات طی تداوم های بالاتر کاهش را نشان می­دهد. در این میان تنها دو استان سیستان و بلوچستان و هرمزگان بیشترین تغییر احتمال تداوم بارش یک تا هفت روزه را تجربه کرده اند. بنابراین تغییرات احتمالی تداوم بارش در نیمه جنوبی کشور عمدتاً کمتر بود.

کلیدواژه‌ها

• ایران
• احتمال تداوم بارش
• تغییرپذیری دهه ای
• روز بارانی

موضوعات

• استخراج، پردازش، تولید و نمایش داده های جغرافیایی

عنوان مقاله [English]

Investigating Decadal Changes in the Probability of Iran’s Precipitation Duration (1977-2016)

نویسندگان [English]

• Zahra Rabiee Gaffar ¹
• Hossein Asakereh ²
• Uones Khosravi ³

¹ Ph.D. Student in Meteorology, University of Zanjan, Zanjan, Iran

² Professor of Climatology, University of Zanjan, Zanjan, Iran

³ Associate Professor of Environmental science, University of Zanjan, Zanjan , Iran

چکیده [English]

Extended Abstract
 Introduction
 The Intergovernmental Panel on Climate Change (IPCC) has reported that climate change results in anomalies, fluctuations or trends in climatic elements, such as precipitation and temperature. In this study, we aim to investigate the decadal changes in the probability of different durations of precipitation in Iran over the past four decades (1977-2016). To achieve this goal, we used the third version of the Asfazari database. We defined a rainy day as a day when the precipitation is more than the average precipitation in a given place. The Markov chain method was employed to estimate the probability of precipitation duration from 1971 through 2016.
Materials and Methods
We adopted the daily data of 2188 stations under the supervision of Iran’s Meteorological Organization for the period 1971 through 2016. Accordingly, we estimated the probability of precipitation duration for 1-7 days for the entire period. We investigated the decadal changes in the probability of precipitation duration for the four study decades and compared them to the whole period under investigation. To understand the spatial features of these changes, we estimated the relationship between changes in the probability of precipitation duration for 1-7 days and spatial factors using multivariate regression models.
Results and Discussion
Our findings revealed that as the duration of rainy days increased, the area affected by precipitation decreased. Therefore, the spatial distribution of the probability of precipitation duration for more than 7 days indicated the smallest area that received precipitation. The probability duration of precipitation lasting 4 days or more throughout Iran was very small, which can be attributed to the effects of local features on precipitation formation. The probability of 1-day precipitation for most regions of Iran was higher than other durations; however, there was only a probability of 1-day precipitation in half of Iran. The highest probability of precipitation duration occurred in the Caspian region, the only region that experienced all durations of precipitation, indicating the presence of various precipitation mechanisms in this area. The greatest probability of decadal changes was observed in the 1-7 day duration in the northern part of Iran, including the northwest to the east of the Caspian Sea and in the south of Alborz Mountain range. Additionally, the most changes in the probability durations of 1-7 days of precipitation in the south have been seen in Sistan and Baluchistan. The lowest probability of decadal changes was shown in large areas of the regions from the east, southeast, and southwest. Therefore, the changes in precipitation durations in the southern half of the regions were generally low; however, in the northern half, the changes were relatively significant.
In general, during the four study decades, the relationship between changes in the probability of 1-7 day precipitation durations and spatial factors, particularly latitude, was positive. Thus, decreasing latitudes resulted in an increasing probability of 1-7 day precipitation.
Conclusion
The most likely changes in precipitation duration were related to the western and eastern coast of the Caspian Sea and the northwestern region of Iran, as well as southern Alborz, where the probability of changes decreased. The least amount of possible changes was related to the south of Iran, where only two provinces, Sistan and Baluchistan, and Hormozgan, experienced the greatest change in the probability of one to seven days of precipitation. Thus, the possible changes in the spatial continuation of precipitation in the southern half of the country were primarily low. However, in the northern half, the possible changes in the duration of precipitation were more significant. changes in the duration of precipitation, along with changes in the intensity and frequency of precipitation, can have significant consequences in extreme events such as droughts and floods. Accurately depicting changes in precipitation duration can be helpful in addressing problems concerning precipitation.

کلیدواژه‌ها [English]

• Iran
• probability duration precipitation
• decadal variability
• rainy day